The present invention, in some embodiments thereof, relates to radiation therapy and, more particularly, but not exclusively, to electron radiotherapy.
Radiation has long been used to treat a variety of cancers by delivering a high local dose of radiation directly to the tumor bed through the operative site. Early radiation treatment methods utilized X-rays as the radiation source. More recent therapy installations have employed beams of high energy electrons as the radiation source to provide a homogeneous dose of radiation with a rapid falloff in radiation intensity beyond the treatment volume, thereby minimizing exposure of non-cancerous tissue to the radiation.
A conventional electron radiotherapy system generally includes a linear electron beam accelerator which accelerates electron to high energy. The high energy electron beam emerging from the accelerator is further processed to produce an electron beam suitable for patient treatment. The patient is placed on a treatment couch that can be precisely positioned to locate the treatment region, which is usually a cancerous tumor or lesion in the patient.
There is generally a difficulty to focus the radiotherapy beam with sufficient precision on the target location. Current medical practice is, therefore, to increase the irradiated area to include additional tissue volume and to increase the dosage of the radiotherapy beam to ensure complete cell death in the target location. The expectation is that all cells in the treated region are killed and possible positioning errors between the beam and the region are compensated. However, such techniques inevitably cause increased collateral radiation damage to the volume abutting the desired region to be treated, in some cases resulting in devastating quality of life effects on the subject.
Known in the art is an electron radiotherapy technique in which a transverse magnetic field is introduced at the target region so as to cause the electrons to spiral in this region and to produce an effective peak in the depth-dose distribution within the tumor volume, thereby to improve the therapeutic dose distribution [Nardi E and Barnea G (1999), Med. Phys. 26(6):967; Nardi et al. (2004), Med. Phys. 31(6):1494; Becchetti ED and Sisterson J M (2002), Med. Phys. 29(10):2435].
U.S. Pat. No. 4,868,843 discloses a radiotherapy system which produces irregular X-ray radiation field shapes so as to shield critical organs not invaded by the tumor. The system includes a multileaf collimator formed of a multiplicity of heavy to metal bar leaves driven relative to a pair of frames which are driven relative to jaws of a rectangular field collimator. A multiplicity of compensators, one attached to each leaf on one of the pair of frames is used to adjust the local intensity of the X-ray radiation within the field. The X-ray beam is limited to a fan with the jaws, the ends and selected parts of the fan are blocked by the multileaf collimator, and the intensity within various portions of the remaining beam is adjusted with compensators. The field of the fan beam is dynamically controlled by these means while the patient table is moved perpendicular to the plane of the fan beam.
Additional background art includes: Bielajew, A. F., “Electron Transport in E and B Fields” in Monte Carlo Transport of Electrons and Photons,” W. R. N. T. E. Jenkins, A. Rindi, A, E. Nahum, and D. W. O. Rogers, editor (1987), Plenum Press, New York. 421-434; and Becchetti, F. D., J. M. Sisterson, W. R. Hendee, and Moderator, “High energy electron beams shaped with applied magnetic fields could provide a competitive and cost-effective alternative to proton and heavy-ion radiotherapy,” (2002) Medical Physics 29:2435-2437.